Not just light: everything is a wave, including you

Not just light: everything is a wave, including you

In 1905, 26-year-old Albert Einstein proposed something quite outrageous: that light could be both a wave and a particle. This idea is as strange as it sounds. How could something be two such different things? A particle is small and confined in a tiny space, while a wave is something that propagates. The particles collide and scatter. Waves refract and diffract. They add up or cancel each other out in superimpositions. These are very different behaviors.

Hidden in translation

The problem with this wave-particle duality is that the language has problems adapting to both behaviors coming from the same object. After all, language is constructed from our experiences and emotions, from what we see and feel. We do not see or feel photons directly. We probe their nature with experimental setups, collecting information via monitors, meters, etc.

The double behavior of photons appears as a response to the way we have set up our experiment. If we have light passing through narrow slits, it will diffract like a wave. If it collides with electrons, it will scatter like a particle. So, in a way, it is our experience, the question we ask, that determines the physical nature of light. This introduces a new element in physics: the interaction of the observer with the observed. In more extreme interpretations, one could almost say that the intention of the experiencer determines the physical nature of what is observed—that the mind determines physical reality. It really is there, but what we can say with certainty is that the light answers the question we ask in different ways. In a sense, light is both wave and particle, and it is neither.

This brings us to Bohr’s atomic model, which we discussed a few weeks ago. His model pins electrons orbiting the atomic nucleus into specific orbits. The electron can only be in one of these orbits, as if it were taking place on a railway track. He can jump between eye sockets, but he can’t be between them. How does it work, exactly? For Bohr, it was an open question. The answer came from a remarkable feat of physical intuition, and it sparked a revolution in our understanding of the world.

The wave nature of a baseball

In 1924, Louis de Broglie, a historian turned physicist, showed quite dramatically that the staircase orbits of the electron in Bohr’s atomic model are easily understood if the electron is represented as consisting of standing waves surrounding the core. These are waves very similar to those we see when we shake a rope that is attached to the other end. In the case of the rope, the standing wave pattern arises due to the constructive and destructive interference between the waves going and returning along the rope. For the electron, standing waves appear for the same reason, but now the electronic wave closes in on itself like an ouroboros, the mythical serpent that swallows its own tail. When we shake our rope more vigorously, the standing wave pattern shows more peaks. An electron in higher orbits corresponds to a standing wave with more peaks.

With the enthusiastic support of Einstein, de Broglie boldly extended the notion of wave-particle duality from light to electrons and, by extension, to any material object in motion. Not only light, but matter of any kind was associated with waves.

De Broglie proposed a formula known as de Broglie wavelength to calculate the wavelength of any matter having mass m moving at high speed v. He associated the wavelength λ with m and v — and therefore to the momentum p = mv — according to the relation λ = h/pwhere h is Planck’s constant. The formula can be refined for objects moving near the speed of light.

For example, a baseball moving at 70 km/ha has an associated de Broglie wavelength of about 22 billionths of a billionth of a billionth of a centimeter (or 2.2 x 10-32 cm). Obviously, there’s not much wiggling there, and we’re justified in imagining the baseball as a solid object. In contrast, an electron traveling at one-tenth the speed of light has a wavelength about half the size of a hydrogen atom (specifically, half the size of the most likely distance between an atomic nucleus and an electron in its lowest energy state).

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While the wave nature of a moving baseball is irrelevant to understanding its behavior, the wave nature of the electron is essential to understanding its behavior in atoms. The crucial point, however, is that everything ripples. An electron, a baseball and you.

Quantum biology

De Broglie’s remarkable idea has been confirmed by countless experiments. In college physics classes, we demonstrate how electrons passing through a crystal diffract like waves, with superimpositions creating dark and bright spots due to destructive and constructive interference. Anton Zeilinger, who shared the Nobel Prize in Physics this year, championed the diffraction of ever-larger objects, from the C to the shape of a soccer ball60 molecule (with 60 carbon atoms) to biological macromolecules.

The question is how life in such a diffraction experiment would behave at the quantum level. Quantum biology is a new frontier, one where the wave-particle duality plays a key role in the behavior of living beings. Can life survive quantum superposition? Can quantum physics tell us anything about the nature of life?

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